I am trying to figure out the initialization process of VASP, and I found an INCAR tag NELMDL, on the wiki page of NELMDL, it is said that VASP requires 5-10 steps to obtain the reasonable orbitals. This seems strange, when setting ISTART=0 and INIWAV=1, the initial charge density is calculated by taking the superposition of atomic charge densities. So I could get reasonable charge density directly, and use it to calculate the reasonable orbitals by just one step.
My question is:
Why does it take 5-10 electronic steps to obtain reasonable orbitals?
Default: NELMDL
= -5 if ISTART=0, INIWAV=1, and IALGO=8
= -12 if ISTART=0, INIWAV=1, and IALGO=48
Description: NELMDL specifies the number of non-selfconsistent steps at the beginning.
If the orbitals are initialized using a random number generator (the
default in VASP), the initial orbitals are usually unreasonable and
the iterative matrix diagonalization will require 5-10 steps to obtain
reasonable orbitals. The charge density corresponding to the initial
orbitals is also, at best, erratic. It is hence advisable to perform a
few electronic steps while keeping the initial Hamiltonian fixed. This
initial Hamiltonian is usually determined from a superposition of
atomic charge densities.
Here are the Schematic representation of the self-consistent loop for the solution of Kohn–Sham equations. I think it would only take just finishing this loop(Electronic steps) one time to get reasonable orbitals.
